(1) Not all crude is the same. Some has much more sulfur.
(2)All commodities are traded on the stock market, and oil is just one of them.
(3) Deals where we buy so much oil from country 'x' to help support their economy.
Yeah! I know. But there is no law - at least that I am aware of - that requires anyone to buy oil on the open market. All are free to contract with suppliers directly if they wish.